Electrochemical Properties Of Li4Ti5O12 Research Articles

Improving the Cyclability and Rate Capability of Li4Ti5O12 Anode Material by Cu2+ and F− co‐Doping

AbstractWe report a new Li4Ti5−xCuxO11.7F0.3 (X=0.1, 0.15, 0.2, 0.25, 0.3) anodic material for use in Li‐ion batteries. These modified Li4Ti5O12 (LTO) materials were prepared by solid‐state method and calcination at 800 °C. The Li4Ti4.75Cu0.25O11.7F0.3 (LTCu0.25OF0.3), among all samples, shows the best results in cyclability and rate ability. The LTCu0.25OF0.3 delivers discharge capacities of 188.8, 180, 169.7, 151.2, 116, and 93.6 mAh g−1 at 0.1, 0.2, 0.5, 1, 3, and 5C, respectively. The capacity retention of LTO, LTOF0.3, and LTCu0.25OF0.3 after 100 charge and discharge cycles at 1C is 90.8 %, 96.3 %, and 97.7 %, respectively. The enhancement in electrochemical performance of LTCu0.25OF0.3 is attributed to the lower polarization and charge transfer resistance (15.5 Ω) and higher Li+ diffusion coefficient (6.4×10−7 cm2 s−1) obtained by cyclic voltammetry (CV) and electrochemical‐impedance spectra (EIS) tests. This work indicates that Cu2+ and F− have a synergistic impact on the electrochemical properties of LTO.

A Novel Strategy toward High‐Performance Lithium Storage of Li4Ti5O12 Using Cu2V2O7 as Additive

Cu2V2O7 is an important material to improve low conductivity of Li4Ti5O12. Herein, Li4Ti5O12/Cu2V2O7 with different Cu2V2O7 ratios is successfully prepared by a liquid phase‐assisted dispersion method. The results show that the electrochemical properties of Li4Ti5O12 are affected by the Cu2V2O7 content incorporated in the composites. Among all obtained samples, Li4Ti5O12/0.05 Cu2V2O7 reveals the best electrochemical performance and capacity retention rate, and its first cycle specific capacity is 246.3/197.2 mAh g−1 when the current density is 30 mA g−1 and it maintains values of 175.8/175 mAh g−1 for 200 cycles between 1.0 and 3.0 V. The resulting Li4Ti5O12/0.05 Cu2V2O7 composite also displays higher capacities at elevated current densities of 120 and 1200 mA g−1, with values always superior to those of the original Li4Ti5O12. The detailed electrode dynamics analysis illustrates that the introduced Cu2V2O7 phase in the composites improves the cycle stability and lithium‐ion transfer rate of Li4Ti5O12. Through in situ X‐ray diffractometry (XRD) test analysis of the Li4Ti5O12/0.05 Cu2V2O7 composite material, it is confirmed that the lithium storage mechanism is improved, where metallic Cu is formed in situ during each charge and discharge reaction process; thereby, the electronic conductivity of the composite material is improved and charge transfer resistance of the bulk material is reduced.

Behavior Investigation of Oxide Electrodes for Li Ion Batteries Viewing from Charge Compensation

Charge compensation resulted defect reactions have played important role on affecting electrical and structural properties of oxides. Depending upon the types of ions available, ionic defects and/or electronic defects are created. For instance, ionic defects tend to enhance the migration of cations/anions. Electronic defects including electrons or hole defects may enhance the electronic conductivity of oxides. For Li batteries, the lithiation of transition metal oxides may be viewed as substitution of Li for transition metal ions. As a result, the lithiation induces the oxidation of Ni, Co ions. Further lithiation may also cause the structural transformation from rock-salt oxide to layered oxides. During a charging/delithiation process at cathode, electron extraction and Li removal from the Li sublattice may be viewed as the creation of electronic/ionic defects. On the contrary, opposite defect reactions including electron injection (or reduction) and lithiation may be observed from the anode. For a high-capacity cathode, Li-rich layered oxides formulated as xLi2MnO3-(1-x)LiMO2(M = Mn, Ni, Co, etc.) show a unique charging plateau around 4.5V. The extraction of electrons is given by rearranged oxygen ions during 1st charging process. In the following discharging as seen in Fig. 1, reduction of Mn+4 from accepting e’ gave a reversible capacity as high as 250 mAh/g. Interestingly, a backward defect reaction was observed in Li4Ti5O12 (LTO) spinel anode during the charging/lithiation process. A self-improving behavior may be explained through accompanying defect reaction. During low-pO2 synthesis, lattice oxygen near surface of LTO tends to be removed with the introduction of Ti+3. As a result, the electron conduction and electrochemical properties of LTO were significantly improved. Finally, the structure transformation of cycled Li-rich oxides from Layered to Spinel structure may be illustrated due to the formation high concentration electronic defects.

Effects of cobalt doping on structural, optical, electrical and electrochemical properties of Li4Ti5O12 anode

Cobalt-doped Li4Ti5O12 (LTO) i.e Li4Ti5−xCoxO12 (x = 0, 0.05, 0.1, 0.15, 0.2) powders have been synthesized by solid state reactions and examined for effects of Cobalt (Co) concentration on structural, optical, electrical and electrochemical properties of LTO. X-ray diffraction (XRD), Raman spectroscopy and field-emission scanning electron microscopy (FESEM) evaluate phase composition and morphology of samples. Optical study reveals reduction in bandgap Eg of LTO from 3.4 to 2.7 eV for x = 0.15, with Eg extension into visible region around 515–740 nm due to increased conduction electrons and energy levels from 3d7 orbitals of Co and induced oxygen vacancies. Electronic conductivity of sample with x = 0.15 increases by 104 as compared to LTO due to conversion of Ti4+ to Ti3+ ions and increased Ti4+-Vo-Ti3+ hopping centers. Ionic conductivity and diffusivity increase upto 2.0×10−7Scm−1 and 4.6×10−12cm2s−1 for x = 0.15, owing to increased lattice spacing by substitution of Ti4+ with Co2+. Frequency dependent conductivity suggests hopping of Li+ ions as dominant conduction in LTO. Thermally activated Li+ ions follow different conduction mechanisms in different temperature regimes. Low activation energies Ea of 0.3–0.5 eV indicate conduction of ions through interstitial pathways i.e 8a-16c-8a. High Ea of 0.7–1.15 eV suggest hopping of ions through vacancy/defect mediated channels or other long routes. Electrochemical tests demonstrate unexpected degradation in electrochemical performance for dilute dopant concentration; x = 0.05 and 0.1, as compared to LTO, which is attributed to substitution of Co2+ ions at Li+ tetrahedral (8a) sites. However, for x = 0.15 electrochemical activity gets better indicating substitution of more of Co2+ ions at Ti4+ octahedral sites.

Preparation and effects of F-doping on electrochemical properties of Li4Ti5O12 as anode material for Li-ion battery

In this work, F-doped Li4Ti5O12 in the form of Li4Ti5O12-xFx (0 ≤ X ≤ 0.4) is successfully synthesized via a solid-state reaction between TiO2 (anatase), Li2CO3, and LiF. The synthesized powder is used as the anode in Li-ion batteries. X-ray diffraction (XRD) results show that the F−-doping does not change the spinel-type structure, and it has successfully doped into the crystal structure of Li4Ti5O12. The morphological and electrochemical characterization of synthesized powders is tested with the scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge-discharge techniques. Among the modified samples, Li4Ti5O11.7F0.3 delivers the highest capacity and cyclability. The Li4Ti5O11.7F0.3 (LTOF0.3) has a capacity of 139.7 and 134.7 mAh g−1 in the first and 100th cycles with 1 C, respectively. The retention of capacity after 100 cycles charge and discharge with 1 C for LTO and LTOF0.3 is 90.8 and 96.3%, respectively.

Effect of Mg+2 and Bi+3 co-doping on structural and electrochemical properties of lithium titanium oxide for use as anode material in lithium-ion battery

Abstract This study describes the effect of magnesium and bismuth co-doping on the structure and electrochemical properties of Li4Ti5O12 as potential negative electrode materials for lithium-ion batteries. The substituted spinel cubic Li4-x/2 MgxTi5-x/2BixO12 (X = 0, 0.05, 0.1) (LTO-MB) materials were prepared through facile ball milling assisted solid-state method. Structural analysis revealed that LTO-MB materials have space group Fd3m. Basic structure and phase composition of Li4Ti5O12 does not changed by Mg-Bi co-doping, lattice parameters are slightly increased. No remarkable change in the morphology was observed in the co-doped materials under the magnification of 2 μm. Significant improvement in the rate capability of LTO-MB materials can be observed upon Mg-Bi co-doping. Both co-doped compositions (LTO-MB-05, LTO-MB-1) have shown greater electrochemical performance as compared to pristine LTO-MB-0. The improvement in the electrochemical performance can be attributed to the mechanism by which co-doping increased conductivity and lithium diffusion coefficient. LTO-MB-05 exhibited specific capacity of ~200 mAhg−1 at 0.1C which is greater than LTO-MB-1(180 mAhg−1) and pristine LTO-MB-0 (165 mAhg−1) at same C-rate. Similarly, the higher value of Li+ diffusion constant (4.77 × 10−12 cm2 s−1) and lower charge transfer resistance (18.77 Ω) together with enhanced discharge capacity are proving LTO-MB-05 a good anode candidate for commercialization.

Porous lithium titanate nanosheets as an advanced anode material for sodium ion batteries

Sodium ion batteries (SIBs) have drawn considerable research attention in energy storage systems due to its low cost and the abundance of sodium resource. However, it is still a big challenge to develop advanced anode materials to achieve high-performance SIBs. In this work, we developed porous lithium titanate (Li4Ti5O12) nanosheets by a simple surfactant-regulating hydrothermal method followed by a calcinating process and used as an anode for SIBs. We investigated the effect of hexadecyl trimethyl ammonium bromide (CTAB) on the morphology and electrochemical properties of Li4Ti5O12 in detail and found that the samples regulated by suitable content of CTAB in the synthesis process have a more regular structure and better electrochemical performance. The optimized sample showed high reversible capacities of 158.9 mAh g−1 and 123.2 mAh g−1 at 0.1 A g−1 and 0.5 A g−1, respectively. The superior electrochemical performance may be originated from the unique porous nanosheet structure, which greatly decreases the charge transfer resistance, shortens the ion diffusion path and offers more active sites for sodium storage.

High performance of β-cyclodextrin-derived Li4Ti5O12/C anode composites for lithium-ion battery

Li4Ti5O12/C anode material for lithium-ion batteries were successfully synthesized by two-step calcination and sol-gel method using tetrabutyl titanate, lithium acetate, citric acid, and β-cyclodextrin as starting materials. The microstructure and morphology of the materials were characterized by X-ray diffractometer, scanning electron microscope, and transmission electron microscope. The electrochemical properties of the materials were conducted by constant current charge-discharge test, AC impedance, and cyclic voltammetry. The results show that the prepared Li4Ti5O12/C composites are spinel cubic crystal with good crystallinity and without other impurities. The particle size is between 50 and 200 nm. The electrochemical properties of Li4Ti5O12 are effectively improved by carbon coating. Among these composites, Li4Ti5O12 with 5% carbon coating shows the initial discharge specific capacity of 167.1 mAh/g at 5C and a 93.3% capacity retention after100 cycles. Its reversible capacity remains 125.4 mAh/g after100 cycles at a high charge-discharge rate of 20 C.

Influence of Defect Reaction on Electrical/Electrochemical Behaviors of Oxide Electrodes for Li Batteries

Functional oxides are known to show interesting electrical properties by introduction of desired defect structures. Electrode performance in Li batteries is also highly dependent on its defect reaction through synthesis and/or charging-discharging cycles. For examples, the reversible capacity of layered cathode such as LiCoO2 is limited by its highly defective layered structure when state of charge greater than 50%. On the other hand, capacity of spinel or olivine cathodes shows higher delithiation rate due to better structural stability. In this study, the behavior of Li-rich layered oxide cathode and Li4Ti5O12 (LTO) are investigated and illustrated based on their defect reactions. For examples, the as-received zero-stain anode oxide Li4Ti5O12 shows conductivity as low as 10-9 S/cm and then causes high interface polarization and low rate capability. With proper processing under low pO2, the electron conduction and electrochemical properties of LTO was significantly improved. Such property enhancement may be well illustrated by defect reaction under low pO2 environment. In other words, lattice oxygen near surface of LTO tends to be removed under very low pO2. Consequently, positively charged oxygen vacancy is formed and then charge-compensated by the creation of two negatively charged electrons. These electrons are eventually associated with tetravalent Ti ions. The fast electron pathway is established by the coexistence of Ti+3 and Ti+4 in Ti cation sublattice. Furthermore, Li-rich layer-structured cathode formulated as xLi2MnO3-(1-x)LiMO2(M = Mn, Ni, Co, etc.) during 1st charging process was found to exhibit oxygen oxidation, vacancy formation. In the following discharging, the manganese reduction (or activation) occurred. As a result, a reversible capacity as high as 250 mAh/g was observed (Fig. 1(a)). Such redox reactions may be illustrated by defect chemistry. In other words, during 1st charging, electrons and oxygen was extracted from lattice oxygen with the formation of oxygen vacancies. In the next discharging process, electrons was accepted by cathode oxides accompanied by valence changing of Mn+4 to Mn+3. It is known that typical electrochemical reactions are highly dependent up movement of electrons and ions. With understanding of defect reaction during materials processing and charging/discharging, advanced electrode materials with much improved electrochemical and/or stability may be developed.

Influence of iron doping on structure and electrochemical properties of Li4Ti5O12

Iron doped lithium titanates Li4+z-3yTi5-zFez+yO12 (0≤z+y≤0.3) have been synthesized and characterized by X-ray diffraction, scanning and transmission electron microscopy, 57Fe Mössbauer spectroscopy, and cyclic voltammetry. Their performance as anode materials for lithium-ion batteries was studied in a wide potential range (0.01 − 3V). Rietveld refinements and 57Fe Mössbauer spectroscopy data show that iron cations occupy both tetrahedral 8a and octahedral 16d sites in the spinel structure. At that, iron occupancy of the octahedral sites is approximately twice as much as the occupancy of the tetrahedral ones. Occupancy of octahedral sites by Fe3+ ions increases after cycling. Li4+z-3yTi5-zFez+yO12 (z+y=0.2) exhibits higher electrochemical capacity at high current densities than the pristine Li4Ti5O12. Moreover, capacity of doped material increases after cycling at high current densities.

Enhanced rate performance of lithium titanium oxide anode material by bromine doping

Br-doped lithium titanium oxide (Li4Ti5O12) particles in the form of Li4Ti5Br x O12-x (x = 0, 0.1, 0.2, 0.3, 0.4) are synthesized via a simple liquid deposition reaction, followed by a high-temperature treatment. The effects of bromine (Br) doping on the structures and electrochemical properties of Li4Ti5O12 are extensively studied. It is found that Br atoms can enter the lattice structure and enlarge the lattice parameters of Li4Ti5O12. Although Br doping has not changed the phase composition, obvious effects on the particle’s morphology and size have been observed. Electrochemical test results indicate that the rate capability of Li4Ti5O12 has been evidently improved by Br doping at an appropriate concentration. The as-synthesized Li4Ti5O11.8Br0.2 electrode presents much higher discharge capacity and better cycle stability than that of the other electrodes. The greatly enhanced electrochemical performance of Li4Ti5O11.8Br0.2 may be attributed to the improved dispersion of nanoparticles and increased electrical conductivity.

The synergic effects of Na and K co-doping on the crystal structure and electrochemical properties of Li4Ti5O12 as anode material for lithium ion battery

The effects of Na and K co-doping on the crystal structure and electrochemical properties of Li4Ti5O12 have been comprehensively investigated by means of X-ray diffraction (XRD), neutron diffraction (ND), scanning electron microscope (SEM) and galvanostatic charge–discharge tests. Rietveld refinements of XRD and ND data indicate that the lattice parameters increase with the doping of Na and K, and Na or K prefers to take 8a site (tetrahedral site) in Li3.98K0.01Na0.01Ti5O12. The lattice parameter and unit cell volume of Li3.98Na0.01K0.01Ti5O12 are even larger than that of Li3.98Na0.02Ti5O12 and Li3.98K0.02Ti5O12 indicating a cooperative effect of Na and K co-doping on the enlargement of lattice parameters and unit cell volume. The electrochemical property results demonstrate that Na and K co-doped Li3.98Na0.01K0.01Ti5O12 has a larger reversible capacity and rate capability as anode material for lithium ion battery compared to un-doped Li4Ti5O12, Na-doped Li3.98Na0.02Ti5O12 or K-doped Li3.98Ka0.02Ti5O12, which indicates the significant synergic effect of Na and K co-doping on the improvement of the electrochemical performances of Li4Ti5O12.

Electrochemical properties of citric acid-assisted combustion synthesis of Li4Ti5O12 adopting Cr by the solid-state reaction process

The effects of Cr3+ doping and citric acid combustion on the electrochemical properties of Li4Ti5O12 were systematically investigated. The solid-state reaction process was used to synthesize four samples marked as LTO, C-LTO, LT-Cr-O, and C-LT-Cr-O, respectively. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) techniques were employed to study their structures and morphologies. The cyclic voltammetry (CV) tests, electrochemical impedance spectroscopy (EIS) analysis, and charge–discharge cycling were performed to study their electrochemical performance. The experimental results showed that the C-LT-Cr-O sample exhibited the advantages both of the Cr3+ doping and the citric acid combustion, presented high ordered morphology and high phase purity, and displayed a discharge capacity of 101.3 mAh g−1 with about 91.8 % capacity retention after 1000 cycles at 10C discharge rate. Therefore, the C-LT-Cr-O material is a promising anode material to be used in lithium ion batteries.

Structure Design and Doping Modification of Li4Ti5O12 for Lithium Lion Batteries

Because of its extreme safety and outstanding cycle life, spinel Li4Ti5O12 has been regarded as one of the most promising anode materials for lithium-ion batteries [1]. However, Li4Ti5O12 suffers from poor electronic conductivity, making it a challenge to achieve high capacity at high rates. Due to the superior electron mobility, high surface area and structural stability, carbon materials are expected to be a potential alternative for the conductive phase in lithium ion batteries.Here, we describe a new strategy to the synthesis of three-dimensional (3D) hybrid-structure Li4Ti5O12/carbon for high-performance lithium-ion batteries by liquid deposition technique using carbon nanotubes (CNTs) [2], graphite oxide (GO) [3], porous carbon (PC) [4], carbon black (CB) as matrix, respectively. The intimate contact between the carbon framework and Li4Ti5O12 nanoparticles suppresses the agglomeration and growth of Li4Ti5O12 nanoparticles, and affords a highly conductive matrix for the rapid ionic and electronic conductions.Thereby, the as-prepared Li4Ti5O12/carbon composites exhibit greatly improved electrochemical performance compared with bulk Li4Ti5O12, showing excellent rate capability (120~150 mAh g-1 at 20 C) and cycling performance. The good performance is due to the short diffusion lengths of the Li4Ti5O12 nanoparticles uniformly dispersed on the highly conductive 3D carbon matrix.In addition, Br-doped Li4Ti5O12 in the form of Li4Ti5Br x O12-x (x= 0, 0.1, 0.2, 0.3, 0.4) was synthesized, the effects of Br doping on the structures and electrochemical properties of Li4Ti5O12 were extensively studied. Although Br doping did not change the phase composition, obvious effects on the particles morphology and size were observed. The as-synthesized Li4Ti5O11.8Br0.2 electrode presents much higher discharge capacity (161 mAh g-1 at 5C) and better cycle stability than that of other electrodes.

High rate Li4Ti5O12@C anode material fabricated by a facile carbon coating method

In this study, carbon-encapsulated Li4Ti5O12 particles are prepared by a facile carbon formation strategy. Under the thermal hydrolysis of acetate in Ar atmosphere, Li4Ti5O12 particles are uniformly coated by amorphous carbon layer with the thickness of 4–6nm. The electrochemical properties of Li4Ti5O12@C are characterized as high rate anode material for lithium ion batteries. Electrochemical results show that Li4Ti5O12@C can respectively deliver the reversible lithium storage capacities of 155.0, 134.7 and 60.3mAhg−1 at 20, 600 and 1500mAg−1 in a narrow working window of 1.0–2.0V. Cycled in a broad potential range of 0.5–2.0V, Li4Ti5O12@C remains the reversible charge capacities of 158.2, 134.5 and 114.7mAhg−1 at 20, 600 and 1500mAg−1 with capacity retentions of 91.5%, 97.5% and 100%, respectively. Even working between 0.0 and 2.0V, Li4Ti5O12@C can still display outstanding electrochemical properties with the reversible capacities of 220.2, 200.6 and 205.1mAhg−1 at 20, 600 and 1500mAg−1.

Structure and electrochemical properties of Li4Ti5O12 with Li excess as an anode electrode material for Li-ion batteries

Li4Ti5O12 is a highly promising anode material for use in Li-ion batteries. Herein, Li4Ti5O12 samples are prepared by sintering Li2CO3 and anatase TiO2 with varying Li molar excess. Characterization by AC impedance spectroscopy, X-ray diffraction spectroscopy and scanning electron microscopy is performed. The electrochemical performance, crystal structure and surface morphology are found to be dependent on the Li content. The effect of TiO2 and Li2TiO3 impurities in Li4Ti5O12 on electrochemical characteristics including charge–discharge cycling and the AC impedance spectra is also investigated. These two impurities are found to have different effects on the electrochemical properties of Li4Ti5O12. At a 2% molar Li excess, a high capacity and Li ion diffusion coefficient are achieved.

Effect of freeze-drying and self-ignition process on the microstructural and electrochemical properties of Li4Ti5O12

Crystalline Li4Ti5O12 is synthesized by a method involving the freeze-drying and self-ignition of a gel prepared from titanium isopropoxide, lithium nitrate and hydroxypropylmethylcellulose (HPMC). This synthesis route yields crystalline Li4Ti5O12 particles after calcination at 800°C for 2h. In an alternative route, addition of ammonium nitrate shifts the self-ignition mode from wave-like propagation to simultaneous. Powders with different microstructures are thereby obtained. Electrochemical characterization shows that the best results for Li+ intercalation/desintercalation are obtained for the powder prepared without ammonium nitrate addition. These results highlight the necessity for a control of the self-ignition mode to obtain adequate properties.

Effects of a dopant on the electrochemical properties of Li4Ti5O12 as a lithium-ion battery anode material

Li4Ti5O12 and Al3+ doped Li(4−x/3)AlxTi(5−2x/3)O12 (x = 0, 0.01, 0.05, 0.1, 0.15, 0.2) are synthesized at 750, 850, 950 °C via solid state reaction using TiO2-rutile, Li2CO3 and Al2O3 as precursors. The samples at 850, 950 °C have better phase purity than those at 750 °C. The preliminary charge–discharge cycling test of undoped and Al3+ doped Li4Ti5O12 reveals that the electrochemical performance of the electrode prepared at 850 °C is better than that at 750, 950 °C. Therefore, the optimum calcination temperature is found to be 850 °C. Li(4−x/3)AlxTi(5−2x/3)O12 (x = 0.01, 0.05, 0.1), which is the low Al-doped sample, exhibits a higher discharge capacity and rate performance than the high Al-doped Li4Ti5O12 (x = 0.15, 0.2) sample. The first discharge capacities at 0.2, 0.5, and 1 C are 174.4, 161.9, and 153.8mAhg−1, respectively for Li(4−x/3)AlxTi(5−2x/3)O12 (x = 0.1). These values are similar to those of Li(4−x/3)AlxTi(5−2x/3)O12 (x = 0.01, 0.05). The capacity retention ratio of Li(4−x/3)AlxTi(5−2x/3)O12 (x = 0.01, 0.05, 0.1) is over 99.3% after 30 cycles. The capacity increase and good rate performance in the optimum Al-doped Li4Ti5O12 are discussed in relation to the stability of the spinel structure and the resulting ease of lithium insertion.